1,736 research outputs found
Sacrificial charge and the spectral resolution performance of the Chandra Advanced CCD Imaging Spectrometer
Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the
focal plane instruments on the Chandra X-ray Observatory, suffered radiation
damage from exposure to soft protons during passages through the Earth's
radiation belts. The ACIS team is continuing to study the properties of the
damage with an emphasis on developing techniques to mitigate charge transfer
inefficiency (CTI) and spectral resolution degradation. A post-facto CTI
corrector has been developed which can effectively recover much of the lost
resolution. Any further improvements in performance will require knowledge of
the location and amount of sacrificial charge - charge deposited along the
readout path of an event which fills electron traps and changes CTI. We report
on efforts by the ACIS Instrument team to characterize which charge traps cause
performance degradation and the properties of the sacrificial charge seen
on-orbit. We also report on attempts to correct X-ray pulseheights for the
presence of sacrificial charge.Comment: 9 pages, 7 figures to be published in Proc. SPIE 485
Distances to the high galactic latitude molecular clouds G192-67 and MBM 23-24
We report on distance determinations for two high Galactic latitude cloud
complexes, G192-67 and MBM 23-24. No distance determination exists in the
literature for either cloud. Thirty-four early type stars were observed towards
the two clouds, more than half of which have parallaxes measured by the
Hipparcos satellite. For the remaining stars we have made spectroscopic
distance estimates. The data consist of high resolution echelle spectra
centered on the Na I D lines, and were obtained over six nights at the Coude
Feed telescope at Kitt Peak National Observatory. Interstellar absorption lines
were detected towards some of the stars, enabling estimates of the distances to
the clouds of 109 +/- 14 pc for G192-67, and of 139 +/- 33 pc for MBM 23-24. We
discuss the relationship of these clouds to other ISM features such as the
Local Hot Bubble and the local cavity in neutral hydrogen.Comment: 15 pages, 6 embedded figures, to be published in the ApJ Vol. 516,
No.
Adult Graduate Students\u27 Perceptions of Gender & Race: Implications for Program Development in Rural Communities
The purpose of this study was to assess the existing levels of awareness toward issues of race and gender in graduate students. Implications for curriculum planning are that faculty members should encourage sensitivity to diversity in all of their classes through small group discussions, case studies, presentations concerning racial and gender issues, and readings that encourage multiple views of issues
Composition of the Chandra ACIS contaminant
The Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory
is suffering a gradual loss of low energy sensitivity due to a buildup of a
contaminant. High resolution spectra of bright astrophysical sources using the
Chandra Low Energy Transmission Grating Spectrometer (LETGS) have been analyzed
in order to determine the nature of the contaminant by measuring the absorption
edges. The dominant element in the contaminant is carbon. Edges due to oxygen
and fluorine are also detectable. Excluding H, we find that C, O, and F
comprise >80%, 7%, and 7% of the contaminant by number, respectively. Nitrogen
is less than 3% of the contaminant. We will assess various candidates for the
contaminating material and investigate the growth of the layer with time. For
example, the detailed structure of the C-K absorption edge provides information
about the bonding structure of the compound, eliminating aromatic hydrocarbons
as the contaminating material.Comment: To appear in Proceedings SPIE volume 5165; paper is 12 pages long
with 13 figure
Groundwater nitrate reduction versus dissolved gas production: A tale of two catchments
peer-reviewedAt the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO3â). The efficiency of NO3â removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N2) & nitrous oxide (N2O), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10 km2) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0â32%), high NO3â and comparatively low N2O emission factors (EF5g1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO3 â to N2 occurred in anaerobic conditions, while at intermediate dissolved oxygen; N2O was the dominant reaction product. EF5g1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO3â occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment.Teagasc Walsh Fellowship Programm
Fetal growth and spontaneous preterm birth in highâaltitude pregnancy: A systematic review, metaâanalysis, and metaâregression
Abstract: Objective: To understand the relationship between birth weight and altitude to improve health outcomes in highâaltitude populations, to systematically assess the impact of altitude on the likelihood of low birth weight (LBW), small for gestational age (SGA), and spontaneous preterm birth (sPTB), and to estimate the magnitude of reduced birth weight associated with altitude. Methods: PubMed, OvidEMBASE, Cochrane Library, Medline, Web of Science, and clinicaltrials.gov were searched (from inception to November 11, 2020). Observational, cohort, or caseâcontrol studies were included if they reported a high altitude (>2500 m) and appropriate control population. Results: Of 2524 studies identified, 59 were included (n = 1 604 770 pregnancies). Data were abstracted according to PRISMA guidelines, and were pooled using randomâeffects models. There are greater odds of LBW (odds ratio [OR] 1.47, 95% confidence interval [CI] 1.33â1.62, P < 0.001), SGA (OR 1.88, 95% CI 1.08â3.28, P = 0.026), and sPTB (OR 1.23, 95% CI 1.04â1.47, P = 0.016) in highâ versus lowâaltitude pregnancies. Birth weight decreases by 54.7 g (±13.0 g, P < 0.0001) per 1000 m increase in altitude. Average gestational age at delivery was not significantly different. Conclusion: Globally, the likelihood of adverse perinatal outcomes, including LBW, SGA, and sPTB, increases in highâaltitude pregnancies. There is an inverse relationship between birth weight and altitude. These findings have important implications for the increasing global population living at altitudes above 2500 m
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